1. Technical Field
The present invention relates generally to integrated circuit (IC) processing and testing, and particularly to temperature and condensation control in a chip tester.
2. Description of Related Art
High performance processor chips or integrated circuits (ICs) often must be tested and subsequently sorted based on their performance and matched to a given class of machine. Individual chips are tested prior to installation on modules in machines in order to identify chip failures, allowing higher machine manufacturing productivity and improving product quality. Test equipment developed to support performance, productivity and quality is usually required to meet functional test limits defined by several boundary variables such as chip/module voltage, clock speed, power dissipation, and temperature.
Chip testing often requires the chips to be cooled to low temperatures. For example, some processor chip test requirements establish a need for cooling devices to temperatures as low as −20 C. Accurate temperature control over a wide range of temperatures during chip testing processes allows verification of whether a processor functions, and more specifically how many of its processor cores function. It also detects more of the faulty chips early in the manufacturing process. For example, two conductors can be touching each other with sufficient force that an electrical connection is made, even though the parts are not mechanically interconnected. Such a part may pass tests and reach a customer, but will fail at a higher frequency rate than is acceptable. If a chip is tested at low temperatures, this marginal interconnection may separate, and thereby identify the faulty part.
Similarly, some chip failure modes are found only at elevated temperatures, while other early use failures which might not have occurred until after reaching a customer may be found during testing at elevated temperatures. Varying temperature testing also allows more precise determination of chip speed, helping to minimize the guardband (i.e., extra margin) that is put into the acceptance criteria for a good chip, allowing an increase in the manufacturing yield.
Alternatives to a precisely controlled thermal system result in less thermal control and hence fewer faults are found, and more guardband must be allowed to ensure the chip will function in the customer environment.
However, testing at varying temperature also raises certain problems. For instance, the manufacturing environment in which some chip testers operate contain atmospheric conditions with a dew point of 17 C, for example. Clearly, any tester surfaces exposed to this environment and operating at −20 C contains mechanical components with surface temperatures that are well below the dew point and will cause condensation of the water vapor in the air on those surfaces. Condensed water within the machine could cause electrical shorts, destroying the tester and/or the tested chip or module. In addition, condensed water escaping from the tester would disrupt manufacturing operations due to safety and related issues.